Conditioning lesions before or after spinal cord injury recruit broad genetic mechanisms that sustain axonal regeneration: Superiority to camp-mediated effects

Abstract

Previous studies indicate that peripheral nerve conditioning lesions significantly enhance central axonal regeneration via modulation of cAMP-mediated mechanisms. To gain insight into the nature and temporal dependence of neural mechanisms underlying conditioning lesion effects on central axonal regeneration, we compared the efficacy of peripheral sciatic nerve crush lesions to cAMP elevations (in lumbar dorsal root ganglia) on central sensory axonal regeneration when administered either before or after cervical spinal cord lesions. We found significantly greater effects of conditioning lesions compared to cAMP elevations on central axonal regeneration when combined with cellular grafts at the lesion site and viral neurotrophin delivery; further, these effects persisted whether conditioning lesions were applied prior to or shortly after spinal cord injury. Indeed, conditioning lesions recruited extensively greater sets of genetic mechanisms of possible relevance to axonal regeneration compared to cAMP administration, and sustained these changes for significantly greater time periods through the post-lesion period. We conclude that cAMP-mediated mechanisms account for only a portion of the potency of conditioning lesions on central axonal regeneration, and that recruitment of broader genetic mechanisms can extend the effect and duration of cellular events that support axonal growth.

Low-density Lipoprotein Receptor-related Protein 1 (LRP1)-dependent Cell Signaling Promotes Axonal Regeneration

“…Outgrowth-Double labeling for LRP1 and NF200, a marker for large-diameter neurons (30), demonstrated that LRP1 is expressed by intact adult, large-diameter DRG neurons and some smaller DRG neurons (Fig. 1A).…”

“…In Vitro Studies-Primary cultures of adult F344 L4-L6 DRG neurons were cultured on poly-L-lysine-coated (16.6 g/ml) 12-well plates as described previously (30). Cells were treated with 100 nM RBD, PEX, or GST for 18 or 24 h. In some assays, cells were pretreated with GST-RAP (200 nM) 30 min prior to the addition of LRP1 agonists.…”

Molecular and Cellular Mechanisms of Axonal Regeneration After Spinal Cord Injury

“…In the conditioning lesion paradigm, lesion of the peripheral, but not central DRG axon induces a cascade of signaling events in the axon and neuronal soma that enhances the intrinsic growth state of the neuron (140). Notably, this conditioning lesion also enhances regeneration of the injured central axon branch if performed prior to, or shortly after the central lesion (64,141).…”

“…Injured DRG neurons rapidly activate a transcriptional program of hundreds of genes as early as 1 day postinjury, and the majority of these exhibit sustained expression patterns by 2 weeks postinjury (141, 142) (140,141,(143)(144)(145)(146)(147)(148)(149). Because this gene expression program is not activated upon central axotomy, many groups have endeavored to promote CNS axon regeneration via the exogenous expression of regeneration associated genes or their upstream regulators (2,150).…”

Construction and identification of pIRES2-LIF-NT-3 bicistronic eukaryotic expression vector

“…This study also highlighted that the delivery of 1 growth factor to the CNS may augment the production of other growth factors, thereby sustaining neuronal growth or survival. In another study, continuous infusion of NT-3 into the dorsal spinal cord was reported to promote the growth of sensory axons from a peripheral nerve graft into the dorsal column white matter (Blesch et al, 2012). A variety of axonal populations of the spinal cord respond to neurotrophic factors (Brock et al, 2010).…”